Michael L. Waite

Stratified turbulence dominated by vortical motion

We present numerical simulations of stably stratified, vortically forced turbulence at a wide range of Froude numbers. Large-scale vortical forcing was chosen to represent geophysical vortices which break down at small scales where Coriolis effects are weak. The resulting vortical energy spectra are much steeper in the horizontal direction and shallower in the vertical than typical observations in the atmosphere and ocean, as noted in previous studies. We interpret these spectra in terms of the vertical decoupling which emerges in the strongly stratified limit. We show that this decoupling breaks down at a vertical scale of U/N, where N is the Brunt-Vaisala frequency and U is a characteristic horizontal velocity, confirming previous scaling arguments. The transfer of vortical energy to wave energy is most efficient at this vertical scale; vertical spectra of wave energy are correspondingly peaked at small scales, as observed in past work. The equilibrium statistical mechanics of the inviscid unforced truncated problem qualitatively predicts the nature of the forced-dissipative solutions, and confirms the lack of an inverse cascade of vortical energy.

The Deepening of Tropical Convection by Congestus Preconditioning

Abstract The role of environmental moisture in the deepening of cumulus convection is investigated by means of cloud-resolving numerical experiments. Under idealized conditions of uniform SST and specified radiative cooling, the evolution of trade wind cumulus into congestus clouds, and ultimately deep convection, is simulated and analyzed. The results exhibit a tight coupling between environmental moisture and cloud depth, both of which increase over the course of the simulations. Moistening in the lower troposphere is shown to result from the detrainment of water vapor from congestus clouds, and the strength of this tendency is quantified. Moistening of the lower troposphere reduces the dilution of cloud buoyancy by dry-air entrainment, and the relationship between this effect and increasing cloud depth is examined. The authors confirm that the mixing of water vapor by subgrid-scale turbulence has a significant impact on cloud depth, while the mixing of sensible heat has a negligible effect. By contrast...

The transition from geostrophic to stratified turbulence

We present numerical simulations of forced rotating stratified turbulence dominated by vortical motion (i.e. with potential vorticity). Strong stratification and various rotation rates are considered, corresponding to a small Froude number and a wide range of Rossby numbers

The Mesoscale Kinetic Energy Spectrum of a Baroclinic Life Cycle

\hbox{\it Ro}

Instability and breakdown of a vertical vortex pair in a strongly stratified fluid

spanning the regimes of stratified turbulence (

Stratified turbulence at the buoyancy scale

\hbox{\it Ro}\,{=}\,\infty

Mesoscale Energy Spectra of Moist Baroclinic Waves

) to quasi-geostrophic turbulence (

Stratified turbulence generated by internal gravity waves

\hbox{\it Ro}\,{\ll}\,1

Boundary Layer Dynamics in a Simple Model for Convectively Coupled Gravity Waves

). We examine how the energy spectra and characteristic vertical scale of the turbulence vary with Rossby number between these two regimes. The separate dependence on

Effective eddy viscosity in stratified turbulence

N/f